Planck And Photoelectric Effect
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Planck And Photoelectric Effect






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Planck And Photoelectric Effect Planck And Photoelectric Effect Presentation Transcript

  • Light, Energy, and More October 23, 2007 Chemistry
  • Recap…
    • Electromagnetic Spectrum
    • High Energy
    • Low Energy
    • Wave Nature of Light
  • What’s Going On Here?
  • When we heat metal what happens?
    • Does the wave model of light explain these changes?
      • Does not explain different wavelengths and frequencies at different temperatures
    • What is light?
      • Radiation….what is radiation?
        • Particles or rays of energy
    • What is temperature anyways?
      • The measure of the average kinetic energy of the particles in an object
      • Kinetic Energy vs. Potential Energy
    • Too many questions….
  • Max Planck (1900)
    • German Physicist
    • Began to look for answers
    • Matter can only gain or lose energy in small quantized amounts
    • What’s quantized?
  • Vocab Word!!!
      • Minimum amount of energy that can be gained or lost by an atom
      • The emitted light from a glowing metal is a ENERGY…this energy is quantized
  • If energy is now quantized…how can we determine the amount of energy of a quantum?
    • What is energy measured in?
    • What are we observing?
    • What happens to the color when we increase the temperature (energy)?
      • Proportional or inversely proportional?
    • Now we need a constant…
      • Planck’s constant, h=6.626 x 10^-34 J*s
  • Time to put these words into action!
    • What is the frequency and wavelength electromagnetic radiation that emits 1.68 x 10^-17 J of energy? What type of electromagnetic radiation is this?
    • Wavelength= 1.18 x 10^-8 m
    • Ultraviolet radiation
  • Some questions to answer…
    • What is the color we see?
    • What happens to the energy of the radiation when we increase the frequency, v, of the radiation emitted?
    • Iron at room temp…color and E?
    • Iron with a little heat…color and E?
    • Iron with lots of heat…color and E?
  • According to Planck’s Theory…
    • If we have a given v, matter can emit or absorb E only in whole number multiples of hv (1hv, 2hv, 3 hv…)
    • Matter can ONLY have specific amounts of energy
    • Wall of kids building blocks
      • We can only add or take away in increments of whole blocks…we cannot remove half a block
  • The Big Mystery of the 1900’s…
    • The Photoelectric Effect…
      • What caused these color changes in metals???
  • Photoelectric Effect
    • Electrons (photoelectrons) are emitted from a metal’s surface when a light of a certain frequency shines on the surface
    • Certain specific amounts of energy (what’s this called???) needed to knock out electrons from metal atoms.
  • Albert Einstein (1905)
    • Added onto Planck’s Theory…
    • Called the electron’s emitted, PHOTONS (the little energy packets Planck called quantums)
    • Now… E photon = hv
    • Planck paved the way for the explanation behind the mystery
    • But some one else came into the picture…
  • Now light is not just a wave…
    • Einstein’s Dual Nature of Light
      • Particle and wave characteristics
      • Light is a beam of tiny particles, called photons, acting like a wave
  • NEW WORD!!!
    • Photon
    • A particle of electromagnetic radiation with no mass that carries a quantum of energy
  • What Einstein added…
    • Energy of a photon has a minimum or threshold value to eject photoelectrons
    • What must happen for the photoelectric effect to occur?
      • Energy of a photon (particle of EM radiation) must have the minimum energy requirement to free the electron from the atom of metal
  • Mystery Solved!
    • No matter how long a light of a certain frequency is shone on metal (intensity), electrons will not be ejected unless the minimum amount of energy is shone.
    • Silver metal
      • Photoelectrons ejected when a light with a frequency of at least 1.14 x 10^15 Hz or greater is used
    • Sodium metal
      • Red light
      • Violet light
  • Revised Planck’s Work…
    • Einstein piggy-backed off of Planck’s Theory and we now have…..
  • Time to do a little work….
    • Tiny water drops in the air disperse the white light of the sun into a rainbow. What is the Energy oa a photon from the violet portion of the rainbow if it has a frequency of 7.23x10^14 Hz?
    • E=4.79 x 10^-19 J
      • Energy in a photon of violet light
  • A couple more… 
    • A photon has an energy of 2.93 x 10^-25 J. What is its frequency? What type of electromagnetic radiation is the photon?
    • V=4.42 x 10^8 Hz
    • TV or FM waves
  • Practice makes perfect… 
    • What is the energy of each photon in the following types of radiation?
      • 6.32 x 10^20 Hz
      • 9.50 x 10^13 Hz
      • 1.05 x 10^16 Hz
    • What types of radiation are each?
    • 4.19 x 10^-13 J gamma or x-ray
    • 6.29 x 10^20 J infrared
    • 6.96 x 10^-18 J ultraviolet